Fire resistant compositions

ABSTRACT

An aqueous fire resistance treatment composition consisting of water, sodium silicate, a calcined filler and a latent acid catalyst is disclosed. The composition may be applied to cardboard substrates such as corrugated cardboard. The composition is then cured to provide enhanced fire resistance.

This application is the National Phase of International ApplicationPCT/AU00/01537 filed Dec. 14, 2000, which designated the U.S.

FIELD OF THE INVENTION

This invention relates to fire resistant coatings and to cellulosicmaterials modified with such coatings to render them fire resistant. Theinvention relates also to methods of making cellulosic materials fireresistant.

BACKGROUND OF THE INVENTION

Cellulosic materials such as timber and particle board are widely usedas building materials. There are many cellulosic materials for which itis desirable to have some degree of fire resistance. For example, thereare many building materials which, if rendered at least with some degreeof fire resistance, will slow down the process of a fire containedtherein thus providing essential safety for any occupants thereof. Thesebuilding materials include timber, wall boards of many types; surfacematerials that are placed within a building structure, for example,ceiling tiles. If these materials could be rendered at least partiallyfire resistant, any resulting fire would be of a slow burning nature andthus improve the safety of the occupants of the building.

Cardboard is a cellulosic material that generally has a limited use as abuilding material being usually restricted to use as reinforcing inflush panel doors. However, cardboard offers the desirable properties ofrelatively high strength to weight ratio, especially stiffness, combinedwith low cost. In the case of corrugated cardboard it also offers lowthermal conduction which is attributed to the presence of air entrappedin the corrugated cardboard flutes. Despite these attractive benefits,the use of cardboard has been limited because of its combustibility andlack of adequate fire resistance. By fire resistance it is meant thatcellulosic materials treated as taught within the ambit of thisinvention by the solutions described herein, will exhibit a substantialreduction in the propensity to support a fire.

There have been various attempts to improve the fire resistance ofcellulosic materials. In the case of cardboard material, these haveincluded soaking cardboard panels in aqueous solution of sodiumsilicate. However, such coatings have not proven satisfactory as theyhave poor water resistance. Furthermore, on exposure to flames thecoating can melt or crack exposing the combustible cardboard to theflames.

Dimanshtaeyn, U.S. Pat. No. 5,035,851, Jul. 30, 1991 describes the useof coating solution which includes a silicate, a clay and some inorganicmaterials (e.g. a borate) which can be used to coat metals, woods andfoamed polymeric materials to impart some degree of fire resistancethereto. This is a complicated and expensive solution and acceptableresistance to fire is not always achieved.

Luckanuck in U.S. Pat. No. 5,085,897, Feb. 4, 1992 describes a liquidmixture of silicate and an inert mineral fibre a mineral powder which isused to coat steel beams used within buildings. This solution, whencoated on the steel building materials, is said to help reduce twistingof steel columns and other building materials in a fire. The treatmentdoes not include a reactive calcined filler nor a latent acid catalyst.

Nguyen et al., U.S. Pat. No. 4,888,057, Dec. 19, 1989 describes acomposite fire resistant coating which comprises a mixture of silicatesand silicon carbide powder. It is said that building materials coatedwith these materials are resistant to fire. However, this coating iscomplicated and expensive to use.

U.S. Pat. No. 6,040,057 (Mar. 21, 2000) involves the treatment of acellulosic substrate with an alkali metal treated material to render thealkali metal silicate water insoluble.

U.S. Pat. No. 3,940,516 (Feb. 24, 1976) relates to compositionsconsisting of:

5 to 15% of powdered silicate-oxide sinter or alloy

15 to 35% of an anhydrous powdered alumina silicate

50 to 80% of acid phosphates of aluminium, chromium, magnesium orcalcium.

The above compositions lack alkali metal silicates.

U.S. Pat. No. 5,171,496 (Dec. 15, 1992) discloses wood composites. Thecompositions include blast furnace slag and are cured by heating. Thecompositions are not ordinarily fire resistant but can be rendered suchby modifying the cellulosic materials. The composition without thetreated cellulose is thus not a fire resistant composition. Thesecompositions of this citation are also calcium rich and this isimportant to this reaction mode.

SUMMARY OF THE INVENTION

This invention provides in one form an aqueous fire resistance treatmentcomposition comprising:

water;

a metal silicate selected from an alkali metal silicate or an alkalineearth metal silicate;

a reactive calcined filler;

a latent acid catalyst.

The alkali metal silicate is preferably selected from the groupconsisting of potassium silicate, sodium silicate and lithium silicate.The alkaline earth metal silicate solution is preferably selected fromthe group consisting of beryllium silicate, magnesium silicate andcalcium silicate.

Preferably the metal silicate is selected from the group consisting ofsodium silicate and potassium silicate.

More preferably the metal silicate is sodium silicate.

Preferably the reactive calcined filler is selected from the groupconsisting of alumina and alumino silicates.

In an alternative form this invention provides a method of treatingcellulosic substrates to render them fire resistant by treating thesubstrate with a composition comprising:

water;

a metal silicate selected from an alkali metal silicate or an alkalineearth metal silicate;

a reactive calcined filler;

a latent acid catalyst

and allowing the treatment to dry and cure.

Preferably the treatment includes a dried, cured coating having a filmthickness in the range 50-1000 μm.

In a still further form this invention provides cellulosic materialtreated with a fire resistant composition formed by curing a compositioncomprising:

water;

a metal silicate selected from an alkali metal silicate or an alkalineearth metal silicate;

a reactive calcined filler;

a latent acid catalyst.

Preferably the cellulosic material is coated with the fire resistantcomposition.

DETAILED DESCRIPTION OF THE INVENTION

Sodium silicate is the preferred metal silicate. However, other metalsilicates may be used including mixtures of different metal silicates.

The preferred sodium silicate is manufactured by PQ Industries. Thismaterial is an aqueous solution which is basically comprised ofSiO₂/Na₂O.

Examples of suitable solutions of sodium silicate are Vitrosol N andVitrosol H, both available from PQ Australia. Vitrosol N is a 38% w/wsolution in water.

The reactive calcined filler is preferably selected from calcinedalumina and calcined alumino silicate. These materials fall into theclass of fillers known as pozzolans. These are defined as materialswhich in finely divided form and in the presence of water, chemicallyreact with calcium hydroxide at ordinary temperatures to form compoundshaving cementitious properties. Examples of suitable materials arecalcined flint clay, calcined alumina, fly-ash and blast furnace slag.The filler is described as reactive in that it can react with alkalinewater and/or the metal silicate. The filler is thus distinct fromconventional fillers such as talc and clay. These reactive fillers arereadily available and generally of low cost. Fly-ash is a finely dividedglossy material generated from combustion of pulverised coal in modernpower plants. They have previously found use in modified concretes wherelower costs and higher long term strengths can be achieved. The particlesize of the reactive fillers is important for best results and these areachieved when the maximum particle size is less than 150 μm. Generallybetter results are achieved with smaller particles and those that passthrough a 75 μm sieve produce improved performance.

The latent acid catalyst is preferably a modified organic acid,especially an ester, which becomes active under the conditions oftreatment with the composition. Preferred latent acid catalysts areesters of acetic acid and esters of dibasic acids such as glutaric,succinic and adipic. An example of suitable latent acid catalysts isglycerol triacetate. Under the alkaline conditions of the compositionthe ester group hydrolyses leaving free acid which acts as the catalyst.Various other substances, such as phosphates and borates, will alsohydrolyse in the aqueous, alkaline mixture of the invention, in theprocess reducing the pH and causing the mixture to set. An example ofsuch latent catalysts is trisodium meta phosphate. The use of latentacid catalysts allows adequate pot-life to allow the treatmentcomposition to be applied onto the surface. The selection of latent acidcatalyst allows the reaction time to be adjusted to give adequatepot-life for the method of application. Generally, the dibasic acidcatalysts give slower set and longer pot-life than the glyceroltriacetate. Latent catalysts are materials which do not act as catalyststhemselves or are relatively inactive but are converted to catalysts ormore active catalysts by means of chemical or physical changes. Itshould be noted that, in the context of this patent, a latent catalystincludes any substance that, when added to the alkaline mixture of theinvention, chemically or physically changes to a substance that reducesthe pH of the mixture, causing the mixture to set. Such substances arepreferably added in anhydrous form, in which case they often absorbexcess moisture in the formulation, thus speeding the drying of thefinished produce A further example of a latent catalyst is the use ofcarbon dioxide, preferably present in the atmosphere, or supplied via apressure vessel. The carbon dioxide can form carbonic acid on absorptioninto the composition thereby causing the composition to set. A furtherexample of a latent acid catalyst is one that becomes activated byincreasing the temperature of the composition.

The relative properties of the constituents of the compositions of thepresent invention influence the properties of both the liquid and curedcoatings. To enable application by dipping or flow coating it isimportant that the composition have relatively low viscosity.Viscosities in the range of 150-250 cps have been found to beparticularly suitable. However, viscosities considerably in excess of250 cps can be used. For example, viscosities of 2500 cps or more may besuitable, especially if the composition is shear thinning orpseudoplastic. Shear thinning rheology is well known and ischaracterised by a reduction in viscosity as the shear rate increases.The viscosity of the sodium silicate solution as modified with thefiller is often suitable without further adjustment. However, additionalrheology modifying agents, both organic and inorganic may beincorporated to adjust the rheology.

The weight ratio of reactive calcined filler to the metal silicate isnormally in the range of 4:1 to 1:4, preferably 3:1 to 1:3 and morepreferably 2:1 to 1:2. However, low levels of reactive filler canproduce useful compositions. These weight ratios are expressed as theweight of reactive calcined filler to the metal silicate as a 38%aqueous solution. When expressed on a non-volatile basis the range 4:1to 1:4 becomes 10:1 to 1:1.5, 3:1 to 1:3 becomes 8:1 to 1:1.1, and 2:1to 1:2 becomes 5:1 to 1:0.8. Relatively high levels of calcined fillercan lead to thixotropic compositions which can be difficult to use withcorrugated cardboard as the cellulosic substrate because the penetrationof the composition into the flutes is poor. The cure rate at high levelsof calcined filler is usually slower and this can be less useful in somecircumstances. The quantity of latent acid catalyst is normally in therange of 1.0-10% of the total composition.

As well as the components specified above, other ingredients may also bepresent. These include surfactants or wetting agents which may effectthe surface tension and surface wetting characteristics of thecomposition as well as the rheology of the composition. Preferredsurfactants are non-ionic in nature and especially preferred are alkylglucosides. The surfactants and wetting agents can also aid thedispersion of the filler.

Inert fillers such as clays and talcs may be used to modify theproperties of the coatings. Other types of fillers may also be used toconfer property enhancement or cost reduction. For example, hollow,glass or ceramic microspheres may be used to enhance thermal and otherinsulation properties. Anhydrous hygroscopic fillers may also be added.An example of such a material is anhydrous silica gel, used indesiccators. A further example is anhydrous sodium sulphate. Dyes andpigments may also be used. The use of these colouring materials canprovide useful guides as to whether the substrate has been treated.

The compositions of the present invention are applied to cellulosicmaterial substrates and the compositions can impregnate and/or form acoating on the substrate. The compositions can then be cured to formfire resistant compositions. The compositions may be applied by any ofthe usual methods for applying liquid compositions and include spray(air and airless), roller and dip coating. The selection of the mostsuitable application method will take into account the shape of thearticle. For substrates formed from corrugated cardboard, conventionalcoating techniques are quite suitable. However, these substrates may betreated before they are assembled. Reinforced cardboard walls areusually made from flat sheets adhered to interleaved corrugated sheets.

The invention will be described by reference to preferred embodimentsdescribed in the following examples where parts are expressed as partsby weight.

EXAMPLE 1

A liquid fire retardant composition was prepared from the followingcomponents:

calcined flint clay (75 μm) 4000 g sodium silicate (Vitrosol N) (38% NV)4000 g water 80 g Alkadet 15 (Huntsman Chemicals) 1 g Dibasic este(DuPont) 160 g

The ingredients were combined by adding with mechanical stirring thewater and Alkadet to the sodium silicate. The finely divided calcinedflint clay was then slowly added under constant stirring. After all thecalcined flint clay had been incorporated the dibasic ester latent acidcatalyst was added to form the final composition. This composition had auseable pot life of one hour at 25° C. The ratio of reactive calcinedfiller to metal silicate was 2.6:1 on a non volatile basis.

EXAMPLE 2

The coating composition of Example 1 was evaluated by coating corrugatedcardboard.

Two pieces of corrugated cardboard sheets, size 250×250×14 mm, weight135 g each, incorporating layers of corrugation, were immersed in thecomposition of Example 1 fully filled. The sheets were then removed andheld vertically until fully drained. This procedure resulted in allcardboard surfaces, including the internal corrugation, being covered bya thin coat of the liquid mixture. The composition also impregnated thecardboard to a certain extent. One of the cardboard pieces was placed ona plastic sheet on a table, and the second piece on top of the first, toform a small panel size 250×250×28 mm. The panels were then left to setovernight. The following day the panel was dry to the touch, with a hardcoating. The weight of the panel was 890 g. The film thickness wasapproximately 500 μm.

EXAMPLE 3

In this Example the coated cardboard from Example 2 was tested for fireresistance.

Coated cardboard from Example 2 was aged for 10 days at room temperatureand tested by placing it on a gas burner and exposed to the flame forone hour. The temperature on the sample side not exposed to the flamewas recorded every 5 minutes. The results are as set out in Table 1:

TABLE 1 Temperature on Time (Minutes) Unexposed Side 5 25° C. 10 52° C.15 75° C. 20 81° C. 25 89° C. 30 100° C. 35 131° C. 40 140° C. 45 140°C. 50 140° C. 55 141° C. 60 141° C.

The above readings represent very favourable results. If replicated in afull scale fire test to AS 1530.4 a one hour fire rating would have beenobtained, on account of both the low temperature and complete structuralintegrity of the unexposed side. This is a remarkably good result for acardboard panel coating with only thin (generally less than 1 mm thick)layers of the mixture of the invention. In particular, given therelatively high content of water and sodium in the mixture, it issurprising the bulk of the coating did not blister or crack, leading torapid heat penetration and fire test failure.

EXAMPLE 4

This is a comparative example where the composition has no calcinedfiller present. A liquid composition was prepared form the followingcomponents:

Sodium Silicate (Vitrosol N) (38% NV) 9000 g Alkadet 15 (HuntsmanChemicals) 1 g Dibasic ester (DuPont) 360 g

The three compounds were thoroughly mixed using a mechanical stirrer, asin Example 1.

EXAMPLE 5

The coating composition of Example 4 was evaluated by coating corrugatedcardboard.

Two pieces of corrugated cardboard sheets, size 250×250×14 mm, weight135 g each, incorporating three layers of corrugation, were immersed inthe composition of Example 1 until fully filled. The sheets were thenremoved and held vertically until fully drained. This procedure resultedin all cardboard surfaces, including the internal corrugation, beingcovered by a thin coat of the liquid mixture. The composition alsoimpregnated the cardboard to a certain extent. One of the cardboardpieces was placed on a plastic sheet on a table, and the second piece ontop of the first, to form a small panel size 250×250×28 mm. The panelswere then left to set overnight. The following day the panel was touchdry, with a hard coating. The weight of the panel was 624 g. The filmthickness could not be determined as it was colourless.

EXAMPLE 6

In this Example the coated cardboard from Example 5 was tested for fireresistance.

Coated cardboard from Example 5 was aged for 10 days at room temperatureand tested by placing it on a gas burner and exposing it to the flamefor 17 minutes. The temperature on the sample side not exposed to theflame was recorded The results are as set out in Table 2:

TABLE 2 Temperature on Time (Minutes) Unexposed Side 3 29° C. 5 43° C. 857° C. 10 68° C. 13 105° C. 15 170° C.

The above readings are not favourable. If replicated in a full scalefire test to AS 1530.4 a fire rating of less than 15 minutes would havebeen obtained, because of thermal insulation failure at this time.

Examination of the sample after the fire test revealed that the internalcorrugation was heavily fragmented, with numerous cracks allowing arapid flow of heat through the panel.

EXAMPLE 7

This example illustrates the incorporation of ceramic microspheres intoa fire resistant composition according to the invention.

A liquid, fire resistant composition was prepared from the followingcomponents:

calcined flint clay 300 kg sodium silicate (Vitrosol N) (38% NV) 300 kgwater 60 kg Envirospheres SLG 30 kg Alkadet 15 0.06 kg Dibasic ester10.2 kg

The ingredients were combined by adding with mechanical stirring thewater and Alkadet to the sodium silicate solution. The finely dividedcalcined flint clay and Envirospheres were then slowly added underconstant stirring. After these components had been incorporated thedibasic ester latent acid catalyst was added to form the finalcomposition.

EXAMPLE 8

The coating composition of Example 7 was evaluated by coating corrugatedcardboard. 20 pieces of corrugated cardboard sheets, size 2400×1200×14mm, weight 6.1 kg each, incorporating 3 layers of corrugation, wereimmersed in the composition of Example 7, drained for a short time, thenturned upside down to ensure the liquid mix would cover all areas ofcorrugation. The boards were drained, then stacked horizontally,separated by a 3 mm thick plastic grid between all units to allow airaccess, and therefore reduce the drying time.

The boards were weighed after 7 days, showing an average weight of 25.2kg. The coating in the flutes had a thickness of about 250 μm.

EXAMPLE 9

A wall unit size 3.23×3.68 m was constructed using 2 layers of coatedcardboard from Example 8 on each side of a 90 mm steel stud frame, withfibre glass insulation in the core. This frame is of a design commonlyused in housing the studs being spaced 600 mm apart.

The wall was then tested for its effectiveness as a barrier to soundpenetration. An excellent value of STC=54 was obtained, comparingfavourably with plaster board and fibre cement boards on equal weightbasis.

EXAMPLE 10

A wall unit was constructed as per Example 9 except that the surfacearea was smaller, being 1.1×1.1 m. The unit was subjected to a fire testthat gives an indicative fire rating to AS1530.4. The test assesses theperformance of the wall with regard to structural integrity and thermalinsulation. A very good result was obtained in that it took 110 minutesto reach an average temperature of 160° C. on the unexposed side of thewall unit. If replicated in a full scale test to AS1530.4, a fire ratingof 1½ hours would be obtained.

EXAMPLE 11

This example illustrates the use of fly ash as the reactive calcinedfiller.

A liquid fire retardant composition was prepared from the followingcomponents:

Gladstone Fly Ash (Pozzolanic Enterprises Pty Ltd) 4000 g Sodiumsilicate (Vitrosol N) (38% NV) 4000 g Water 600 g Alkadet 15 (HuntsmanChemicals) 1 g Dibasic ester (DuPont) 160 g

The ingredients were combined by adding with mechanical stirring thewater and Alkadet to the sodium silicate. The finely divided Fly Ash wasthen slowly added under constant stirring. After all the Fly Ash hadbeen incorporated the dibasic ester latent acid catalyst was added toform the final composition.

EXAMPLE 12

The coating composition of Example 11 was evaluated by coatingcorrugated cardboard.

Two pieces of corrugated cardboard sheets, size 250×250×14 mm, weight135 g each, incorporating three layers of corrugation, were immersed inthe composition of Example 11 until fully filled. The sheets were thenremoved and held vertically until fully drained. This procedure resultedin all cardboard surfaces, including the internal corrugation, beingcovered by a thin coat of the liquid mixture. The composition alsoimpregnated the cardboard to a certain extent. One of the cardboardpieces was placed on a plastic sheet on a table, and the second piece ontop of the first, to form a small panel size 250×250×28 mm. The panelswere then left to set overnight. The following day the panel was dry tothe touch, with a hard coating. The weight of the panel was 994 g.

EXAMPLE 13

In this Example the coated cardboard from Example 12 was tested for fireresistance.

Coated cardboard from Example 12 was aged for 10 days at roomtemperature and tested by placing it on a gas burner and exposing it tothe flame for one hour. The temperature on the sample side not exposedto the flame was recorded every 5 minutes. The results are as set out inTable 3:

TABLE 3 Temperature on Time (Minutes) Unexposed Side 5 26° C. 10 56° C.15 78° C. 20 85° C. 25 94° C. 30 106° C. 35 130° C. 40 142° C.

Temperature on Time (Minutes) Unexposed Side 45 143° C. 50 144° C. 55144° C. 60 145° C.

The above readings represent very favourable results being very similarto Example 2, and showing that calcined flint clay can be replaced withlower cost Fly Ash.

EXAMPLE 14

A liquid fire retardant composition was prepared from the followingcomponents:

Calcined flint clay (75 μm) 6000 g sodium silicate (Vitrosol N) (38% NV)3000 g water 1200 g Alkadet 15 (Huntsman Chemicals) 1 g Dibasic ester(DuPont) 120 g

The ingredients were combined by adding with mechanical stirring thewater and Alkadet to the sodium silicate solution. The finely dividedcalcined flint clay was then slowly added under constant stirring. Afterall the calcined flint clay had been incorporated the dibasic esterlatent acid catalyst was added to form the final composition. The ratioof reactive calcined filler to metal silicate calculates as 5.2:1 on anon volatile basis.

EXAMPLE 15

The coating composition of Example 14 was evaluated by coatingcorrugated cardboard.

Two pieces of corrugated cardboard sheets, size 250×250×14 mm, weight135 g each, incorporating three layers of corrugation, were immersed inthe composition of Example 14 until fully filled. The sheets were thenremoved and held vertically until fully drained. This procedure resultedin all cardboard surfaces, including the internal corrugation, beingcovered by a thin coat of the liquid mixture. The composition alsoimpregnated the cardboard to a certain extent. One of the cardboardpieces was placed on a plastic sheet on a table, and the second piece ontop of the first, to form a small panel size 250×250×28 mm. The panelswere then left to set overnight. The following day the panel was dry tothe touch, with a hard coating. The weight of the panel was 1060 g.

EXAMPLE 16

In this Example the coated cardboard from Example 15 was tested for fireresistance.

Coated cardboard from Example 15 was aged for 10 days at roomtemperature and tested by placing it on a gas burner and exposing it tothe flame for one hour. The temperature on the sample side not exposedto the flame was recorded every 5 minutes. The results are as set out inTable 4:

TABLE 4 Temperature on Time (Minutes) Unexposed Side 5 28° C. 10 50° C.15 80° C. 20 145° C. 25 162° C. 30 170° C. 35 182° C. 40 189° C. 45 193°C. 50 194° C. 55 194° C. 60 195° C.

While the result is not quite as favourable as Example 3, it is stillvery good, especially in view of the fact that the unexposed side of thepanel did not change in appearance, and all six coated layers ofcorrugation remained essentially intact. Thus, it is clear that thepanel made as per Example 15 is capable of acting as a fire barrier,significantly slowing the progress of a fire.

Since modifications within the spirit and scope of the invention may bereadily effected by persons skilled in the art, it is to be understoodthat the invention is not limited to the particular embodimentdescribed, by way of example, hereinabove. As a further example of theuse of compositions of the present invention, these may be used in aprocess for preparing the cellulosic substrate, especially cardboard.Therefore rather than post treating cardboard with the composition ofthe present invention the cardboard is prepared in the presence of thecomposition.

What is claimed is:
 1. An aqueous fire resistance treatment compositioncomprising: water; a metal silicate selected from an alkali metalsilicate or an alkaline earth metal silicate; a reactive calcinedfiller; a latent acid catalyst.
 2. An aqueous fire resistance treatmentcomposition as defined in claim 1 wherein the metal silicate is selectedfrom the group consisting of potassium silicate, sodium silicate andlithium silicate.
 3. An aqueous fire resistance treatment composition asdefined in claim 1 wherein the metal silicate is selected from the groupconsisting of beryllium silicate, magnesium silicate and calciumsilicate.
 4. An aqueous fire resistance treatment composition as definedin claim 2 wherein the metal silicate is selected from the groupconsisting of sodium silicate and potassium silicate.
 5. An aqueous fireresistance treatment composition as defined in claim 4 wherein the metalsilicate is sodium silicate.
 6. An aqueous fire resistance treatmentcomposition as defined in claim 1 wherein the calcined filler iscalcined alumina or calcined alumino silicate.
 7. An aqueous fireresistance treatment composition as defined in claim 6 wherein thecalcined filler is selected from the group consisting of calcined flintclay, calcined alumina, fly-ash and blast furnace slag.
 8. An aqueousfire resistance treatment composition as defined in claim 7 wherein thecalcined filler is selected from the group consisting of calcined flintclay, calcined alumina and fly-ash.
 9. An aqueous fire resistancetreatment composition as defined in claim 1 wherein the calcined fillerhas a particle size less than 150 μm.
 10. An aqueous fire resistancetreatment composition as defined in claim 1 wherein the latent acidcatalyst is a carboxlic acid ester.
 11. An aqueous fire resistancetreatment composition as defined in claim 1 wherein the relative weightproportions of reactive calcined filler to metal silicate is in therange 10:1 to 1:1.5.
 12. An aqueous fire resistance treatmentcomposition as defined in claim 11 wherein the relative weightproportions of reactive calcined filler to metal silicate is in therange 8:1 to 1:1.1.
 13. An aqueous fire resistance treatment compositionas defined in claim 12 wherein the relative weight proportion ofreactive calcined filler to metal silicate is in the range 5:1 to 1:0.8.14. A cellulosic substrate treated with a composition as defined inclaim
 1. 15. An cellulosic substrate as defined in claim 14 wherein acoating of film thickness 50-1000 μm is formed on the substrate.
 16. Amethod of enhancing the fire resistance of a cellulosic substrate bytreating it with a composition as defined in claim 1.